The image was presented as a graphic illustration of the cost of human trafficking, as a senior officer said society needed to grasp the horror of the crime.

Detective Superintendent Philip Marshall said police in Northern Ireland had rescued 73 victims of human trafficking over the last two years - though the meeting heard the figure is only the tip of the iceberg.

The officer, from the police service's Organised Crime branch, said human trafficking was modern day slavery and had to be tackled.

"Prostitution must be addressed by all sections of the community," he told the meeting.

"We must raise awareness and change the mindset of society."

He said of human trafficking: "It is something that we should not only be concerned about, it is something that we should be very angry about.

"It is estimated that globally, between two to four million people are trafficked across borders and within their own countries every year.

"And it is believed to be the third largest source of income for organised crime."

He said the most common form of trafficking in Northern Ireland is for sexual exploitation.

The Police Service of Northern Ireland worked with other police services to tackle a crime which ignored borders, he said.

And the detective said women, and in some cases transsexuals, had been trafficked into Northern Ireland from around the globe.

He showed the meeting a photograph of a terraced house in Belfast where police had uncovered a brothel.

A second photo showed a door inside the building which had a lock fitted to the outside of it.

The picture of the inside of the door showed marks where the woman trapped inside, and forced into prostitution, had tried to claw her way out.

He detailed police efforts to combat the crime.

"But it is apparent from victim and suspect interviews that there is an increased demand for sexual services in Northern Ireland which is attracting organised crime gangs and this leads to the trafficking of victims and their exploitation to fill the market demand."

He added: "What we must do is challenge the myth and outline the reality."

The officer challenged society not to see prostitutes as "working girls", but victims who found themselves targeted not by "punters", but by exploiters or rapists.

He said that if society rejected the exploitation of women in prostitution, they would by extension combat the misery of human trafficking.